A benzaldehyde compound of formula (4):
(wherein Q represents a hydrogen atom or a halogen atom, and Ar represents a phenyl group optionally substituted with at least one selected from the group consisting of alkyl groups having 1 to 4 carbon atoms and halogen atoms.)is useful as a production intermediate of a disinfectant (see, e.g., JP-A No. 9-95462 and U.S. Pat. No. 5,145,980).
Regarding a method for producing a benzaldehyde compound of formula (4), JP-A No. 9-95462 discloses a method of oxidizing a corresponding benzyl halide compound and U.S. Pat. No. 5,245,980 discloses a method of oxidizing a corresponding benzonitrile compound.